Impregnated wood and process of treating wood



Patented Nev. 5, 1929 UNITED STATES PATENT OFI'CE" osnrn nannorrn cooLmGE, SD, or 3300mm, massnorrusnrrs, 'nssrenon. 'ro 7 mon'rnn, INC., on BosroN, Mnssncnu-snrrs, a oonronn'rron or massnonusnr'rs mrnnana'rnn woon AND rnocnss or resume woon No Drawing. Application filed April 5, 1927,

attention for many years. Of the various treatments which have acquired wide commereial use, the impregnation with creosote oil has been the most successful and is today the treatment used most extensively. Other 10 impregnating agents have, however, been used to a very considerable extent. For example, zinc chloride has been widely used, while borax and many of the arsenates and other poisonous salts, although well known in this connection, have been used less commonly.

While creosote appears to be the most effective preservative in common use, its disagreeable odor, its tendency to ooze from the wood, and the fact that paints and'varnishes do not stick on a creosoted surface, obviously render wood treated with this material unsuited for a great variety of uses. For these uses a treatment with one of the salts having toxic properties, such as zinc chloride or borax, is preferable. The difficulty with such treatments, however, 'is that practically, if not .quite all, of the common substitutes for creosote are very soluble in water and they leach gradually from the. wood. Some of these salts will even absorb suflicient moisture from or the like, to dissolve and form. a disagreeable streak of whitish appearance underneath the varnish. Furthermore, when wood treated with these salts is exposed to the weather, it loses its impregnating agents very rapidly, so .that after a time the quantity of impregnating material left in the wood is insuflicient to protect it. This objection also'applies 1n a lesser degree to creosote. The present invention relates to the impregnation of wood for the purpose of preserving'it or otherwise increasing its usefulness, and it has for.its general object to devise a treatment which will overcome the objections above mentioned, while at the same time being economical and thoroughly practical. The invention also involves a novel roduct.

An important feature of the invention consists in the treatment of wood with any suitthe atmosphere through a coating of varnish Serial No. 181,270. Renewed April 13, 1929.

able preservative agent, preferably one or more of the cheaper salts, andthe protection of the salts with an a ent which will prevent them from leaching min the wood.

According to a preferred process, the wood is first impregnated with a'toxic or preservative agent such for example, as zinc chloride or b'orax, and combined with this agent is a salt, such as aluminum sulphate, which will combine with the material used in a subsequent impregnation. This initial impregnation may be performed in any convenient manner, and in accordance with the well.

known processes of impregnating wood.

Assuming, for example, that the wood under treatment is red oak in small dimensions, a satisfactory impregnation can be obtained by immersing thewood in a solution of the salts and maintaining a gressure of approximately two hundred poun 5 per s uare inch on the solution for one hour, the so ution preferably being held at a fairly high temperature, as for example, 175 to 200 F.'- A five to ten per cent solution of these salts in water is' suitable for this step of the process buthigher concentrations may be used. The impregnation should be performed in a pressure cylinder of the type used in .impreg'natin wood: When'this step has been compTete it is preferable to cut off the supply of steam to the cylinder and then to circulate cold water through the steam heating coils in the cylinder. This operation should be continued for about one hour, the consequent cooling of the solutionresulting in precipitatin 01' (mncentrating the SaltS Hl the wood. Oiviously theexact procedure adopted necessarily will depend somewhat upon the equipment avail-' able, the kind of wood being treated, the size of the pieces being treated, and other con-- siderations with which those skilled in this art are familiar.

If the impregnation is performed at high v temperatures there is considerabletenden'cy to darken the .wood, but this discoloration can be reduced or entirely avoided by reducin the temperature at which the treatment is performed. A high temperature followed by cooling, as above described, is a convenient method of introducing a high concentration too I se uent' treatment. This may be accom-' plished either by subjecting the wood to a vacuum while it still remains in the treating cylinder, or the wood may be removed and partially dried in a kiln or in the air.

According to this process the wood prev i.

ously treated with salts is now impregnated with a solution ,of soap, ordinary laundry soap being satisfactory. A solution of one part of ordinary soap in five parts of water can be used with good results. In view of the fact that ordinary soap contains considerable water, in some cases as high as 40%, it is preferable to .use soap from which the water has been practically eliminated, and in such case a solution made by dissolving one part of dry soap in ten parts of water is satisfactory. This impregnation should be pergtormed in a pressure cylinder, the solution being kept hot,

at say 150 F., and forced into the wood under pressure. A pressure of approximately two hundred pounds for a period of one hour usually is sufiicient. The wood then is .removed from the cylinder and stackedwhere it can drain and dry out.

When the first impregnation is made with a mixture of salts, such as above described, the soap which is introduced in the second step of the process combines with the alumihumsulphate and produes an insoluble metallid soap which acts as a sealing or protec-' tive agent for the toxic salts introduced in the first impregnation. The action appears to be that the impregnation with the salts results in depositing these salts in the walls of the pores and tracheids of the wood and also on the surfaces of said walls. The sub sequent impregnationwith soap apparently results in forming an insoluble soap coating on the walls, which coatingprotects the salts.

- It may be also that some of the soap, either soluble or insoluble, plugs or seals the tracheids. While this is the best explanation which I can give at this time, it should be understood that the invention is not limited to the theory above advanced.

It will be obvious to those familiar with the manufacture of insoluble soaps that salts" other than aluminum sulphate can he successfully used in this process. This particular salt has'been mentioned as an example of this class of salts, and also because it has been found in practice to work satisfactorily.

which later is introducedto produce a metal lic soap, but it is preferable to use aluminum sulphate with the zinc chloride because it produces a better seal than does the zinc chloride." Other toxic salts also can be used, as has been mentioned above.

It is not necessary to remove the wood from the cylinder between impregnating steps in the, process above described, or, in fact, to withdraw any of the water introduced in the first impregnation, provided some care is exercised inconducting this step of the process.

Assuming, for example, that dry red oak is being impregnated, it is entirely possible to force into the wood a Weight of salt solution equal to the weight of the wood. It is not necessary for most purposes, however,

to carry the impregnation to this point, and

satisfactory results can be produced by sto ping the first impregnation when the weig t of the wood has been increased by approximately 60%. washed out with .cold water,- the pressure being maintained during this washing operatio'n. The, soap solution next' is admitted to the cylinder, and the second step of the rocess is started at once. A sufiicient weig t of the soap solution should be forced into the wood so that the dry weight of the soap introduced will be about threetimes the dry weight of the aluminum sulphate. While this process thus involves two steps or movements, it requires only one handling of the wood.

Many variations in the method above described are available within the scope of the invention. For example, under some circum-' stances it may be sufiicient to use in the first impregnation simply a solution of a-salt or The cylinder may then be salts which will combine with the soap' so that an impregnation chiefly-or entirely with insoluble soap finally results. Also, the steps under some conditions maybe reversed, a salt treatment following a soap treatment. In some cases, also. the aluminum sulphate or other salt used for the specific purpose of combining with the soap to form an insoluble soap, may be omitted, the first impregnation being made with a toxic agent, such as borax, and the subsequent impregnation made with a soap solution. lln this case some of the soap may be converted into an insoluble variety due to its combining with certain salts which are present in the commercial borax as im-pur1t1es, but a large part of the soap will remain in a soluble form. Since this soap, even though soluble in water, is mechamcally confined in the pores and tracheids of the wood,- there is very little opportunity for the action of atmospheric moisture 'on it,

so that for some purposes this soluble soap seal atl'ords ample protection, for the more readily soluble salts.

Essentially the same process can also be used in protecting other preservative agents,

such as creosote. For example, the wood can be given an empty cell treatment with creosote and some of the disagreeable features of the wood so treated can be eliminated by subiso sequently impregnating it with'water soluble v the ingredient necessary to act-on the soap or salt to produce an1insoluble soap. In some cases, also, particularly where it is desirable to obtain an unusually high con centration'of the toxic salts inthe'wood, it may be preferable to confine the impregnations necessary to produce the insoluble soap to the outer strata of the Wood where its function as a sealing agent is more essential. This permits a high concentration of the toxic salts in the inner strata of the wood.

It will be appreciated that the invention provides a process which may be practiced "very economically, andwhich, at the same time, avoids thevery serious objections above mentioned to the use of certain impregnating 'agents which would beentirely satisfactory if it were not for the fact that they are so readily effected by moisture. The fact that the process can be practiced in any well equipped treating-plant without requiring expensive changesin equipment, is. an important practical advantage. It should be noted that the treatment with certain of the salts above mentioned, particularly borax, substantially reduces the combustibility of the wood, or makes it more or less fire resistant, depending upon the concentration of the salts. And the insoluble soap seal is'equally as valuable in protecting salts which make the wood fire resistant as those designed to prevent decay.

The present application is a continuation ,in part of my earlier application Serial No.

155,766, the broad claims covering subject matter common to the two applications being superficial treatment of surface coating which probably never penetrates the wood for a dept inch.

Having thus described my invention, what of more than one sixty-fourth of an Idesire to claim as new is:

1. An article of the character described "com risin wood im re nated for a substantial depthwith a toxic preservative sealed in the wood by soa v 2, ,An article of the character described comprising wood impregnated for a substantial depth with a toxic preservative sealed i the wood byan insoluble soap.

3. 'An article of the character described comprising wood impregnated for a substantial depth with a water soluble toxic preservative protected by an insoluble soap.

4. An article of the character described comprising wood, the pores and tracheids of whichior a substantial depth are impregnated with a water soluble salt, said pores and tracheids also beingimpregnated with an insoluble soap which serves as a protective agent for said salt.

5. An article of the character described comprising wod, the inner strata of which are impregnated with a toxic preservative, the outer strata being impregnated with an insoluble soap. i

6. An article of the character described comprising wood impregnated for a substantial depth with water soluble salts and with an insoluble soap serving as a protecting agent for said salts.

7. That improvement in processes of treating wood which consists in subjecting the wood tosuccessive 'impregnations with solutions of soap and metallic salt.

8. That improvement in processes of treating wood which consists in subjecting the wood to successive im-pregnations with solutions of soap and a metallic salt capable of combining with said soap to form an insoluble soap.

9. That improvement in processes of treating wood which consists in impregnating the wood with a toxic preservative and a salt adapted to react with a soluble soap to form an insoluble soap, and subsequently impregnating the wood with a solution of a soluble soap to combine with said salt and Yes thereby produce an insoluble soap capable of Y sealing said toxic preservative in the .wood.-,

10. That improvement in the process of treating wood which consists in impregnate ing wood with a solution of a toxic salt and another salt adapted to react with a soluble soap to form an insoluble soap, driving surplus solvent out of the wood and subsequently impregnating the wood so treated with a solution of soap to combine with said second salt and produce an insoluble soap capable of sealing said toxic salt. in the wood.

11. That improvement in the process of treating wood which consists in impregnating wood with a solution of salts, one at least of which has toxic properties, evaporating excess solvent from the wood and subsequently impregnating the wood so treated with a material adapted to combine with one of said salts to form an insoluble soap. 12. That improvement in processes of treating wood which consists in impregnating. the wood with a toxic preservative, and subsequently impregnating the wood so treated withsoap to seal the preservative in the wood. p

13. That improvement in processes of treating wood which consists in subjecting jthe wood to successive impregnations with materials which combine in the wood to form an insolublemetallic soap.

14. That improvement in processes of treating wood which consists in subjecting the wood to successive impregnations with materials which combine in the wood to form an insoluble metallic soap,'and associating a soluble soap to form an insoluble soap, and subsequentl V vtreated wit a solution of soap to combine toxic preservative with one of said impregnating materials. V

15. That improvement in processes, of treating wood which consists in forcing into the pores and tracheids of the wood a water solution of a mixture of protective salts including a metallic salt adapted to react with a.

impregnating the woodso with said metallic salt to produce an insoluble soap capable of sealing said protective salts in the wood.

- JOSEPH RANDOLPH COOLIDGE, lll. 

